Multi-station communications in radio links, buss type wire-links, and other networks such as satellites, have the capability of delivering information to a plurality of receiving stations throughout the network by way of a single transmission. For instance, a satellite transmission generally may be simultaneously received by a plurality of separate and distinct receiving dishes.
A problem of longstanding concern arises when certain receiving stations determine that particular data packets of information received from the distribution station are in error (i.e. missing or jumbled) and require re-transmission. When a plurality of receiving stations simultaneously communicate their re-transmission requests to the central distribution station, these repeat request signals often conflict with one another thus resulting in communication error preventing the desired packets from being re-transmitted from the distribution station. As will be evident to those of skill in the art, such conflicts typically arise when a plurality of receiving stations share the same communication link with the distribution station thus leading to problems of multi-access.
Different types of communication links have typically been used for transfer of data. One type of common carrier communication link is terrestrial such as cable or leased phone lines. Other common carriers may include high speed satellite, microwave, or FM band links. Such links often have different lengths, operate at different error rates, and transfer data packets at different speeds. Because a variety of communication links having different characteristics may be available between two locations, it is advantageous to choose the communication link which is the most economical and efficient for the type of data transfer desired. It is therefore desireable to provide a communication system which is flexible, adjustable, and efficiently used for data transfer over communication links having different characteristics.
Because of the value and precision of data file transfer, it is important that all data be correctly transferred, particularly in the face of predictable errors caused in the communication links used for data transfer. Such errors are often caused, for example, in satellite links by bolts of lighting.
In response to such problems, conventional file transfer protocols (FTPs), such as Transmission Control Protocol/Internet Protocol (TCP/IP), based on a layered architecture have been developed for the transfer of data between remote computers or servers. Such protocols divide files into packets, add error identification data thereto, and then transmit the packets or frames so as to allow evaluation with respect to whether the packets are correctly received. The receiving station analyzes the error identification data and thus identifies packets in error. After such a determination is made as to which packets need to be re-sent, the receiving station typically communicates to the sending station which data frames or packets are in error and requests re-transmission of such frames.
A downside to such systems is that when different receiving stations request re-transmission of different packets, such re-transmission of different packets to different stations via satellite take up valuable satellite time and lengthens the time required to transmit and re-transmit the files to the different receiving stations. Furthermore, the aforementioned problem of multi-access arises when multiple receiving stations simultaneously attempt to request re-transmissions from the distributor via a common link such as a satellite channel, problems of multi-access also lengthening the time period required to transfer files from the distributors to the receiving stations.
U.S. Pat. No. 4,908,828 discloses a method for error-free file transfer and reception wherein a distribution station transmits/transfers files to a plurality of receiving stations. Each file to be transferred is divided into a plurality of data packets, these packets being transmitted from the distribution station to the receiving stations via the SCA band of an FM channel. In an effort to avoid the aforementioned problems which occur when receiving stations request re-transmissions of select packets in error, the distribution station of this patent cyclically re-transmits each packet for a predetermined number of transmission cycles, e.g. five. In other words, each file (made up of a plurality of packets) is transmitted five times. In such a manner, the receiving stations need not request re-transmission if certain packets are in error, they simply need wait for the next transmission cycle originating from the distribution station. Although the system of this patent may well perform satisfactorily, the need for up to five transmission cycles is undesirable in that it unduly ties up costly transmitter time and prevents additional data files from being transferred via the same link.
U.S. Pat. No. 4,422,171 discloses a method and system for data communication between first (sender) and second (receiver) stations. Files to be transferred from the first station to the second in this patent are divided into a plurality of data packets, each packet being transmitted via satellite from the sender to the receiver. The receiver station upon detecting errors in specific packets, transmits requests for re-transmission with respect to these specific packets back to the sender station. Such requests for re-transmission are also by way of satellite, as is the actual re-transmission of packets originally in error. The provision of two-way satellite communication in the data transfer system of this patent requires each station to have its own satellite transmitter and receiver (as opposed to only a receiver or transmitter) thus significantly increasing the cost of the system.
U.S. Pat. No. 5,301,194 discloses a communication system wherein a central office distributes file data in the form of data packets to a plurality of local or receiving offices. Upon detecting packet errors, the receiving offices transmit requests for re-transmission back to the central office with respect to the packets in error, these re-transmission requests being via satellite. Because communication between the central office and the plurality of local offices is solely via satellite, each local office is required to have its own satellite transmitter thus significantly increasing the overall cost of the system.
U.S. Pat. No. 4,841,526 discloses a data communication system wherein data is transmitted via satellite from a first station to a second station. The second station acknowledges correct data packet reception via either a satellite transmission or a telephone link connecting the first and second stations. However, re-transmission of packets originally in error is also done via satellite thereby significantly increasing the time taken for correct transmission of such files.
Another disadvantage of the U.S. Pat. No. 4,841,526 data transfer system arises when the sending station is transferring data to a plurality of receiving station. In such an environment this system re-transmits "different" data packets sequentially to the different receiving stations. For instance, assume that receiving station number 1 requires re-transmission of packet numbers 15-20, and station numbers 2 and 3 require re-transmission of packet numbers 32-50 and 61-64 respectively. Under such circumstances, the distributing or sending station must first transmit packet numbers 15-20 to station 1, then packet numbers 32-50 to station 2, and finally packet numbers 61-64 to station 3. This unfortunately ties up an extremely large amount of costly satellite time and/or bandwidth in that all three re-transmissions cannot be done simultaneously.
It is apparent from the above that there exists a need in the art for a file transfer communication system wherein data files may be transferred in packet form from a distribution station to a plurality of receiving stations (e.g. CATV headends) in a manner such that packets originally transmitted in error may be re-transmitted from the distribution station to the appropriate receiving station while at the same time the receiving station is still receiving packet data via satellite. Additionally, a need exists for different data packets to be simultaneously re-transmitted to different receiving stations. It would also be desireable if such a system were to avoid having a satellite transmitter disposed at each receiving station so as to reduce the overall cost of file transfer.
It is the purpose of this invention to fulfill the above-described needs in the art, as well as other needs apparent to the skilled artisan from the following detailed description of this invention.